In the past few decades, technological advances have made the use of vacuum florescent (VF) displays an aesthetically pleasing and relatively inexpensive alternative to back-lit displays. Examples of electronic systems and components utilizing such VF displays include entertainment systems, such as video and audio systems, kitchen appliances, such as conventional and microwave ovens, and automotive systems, such as automotive entertainment systems and instrument clusters, to name a few.
One specific example of an automotive electronic system utilizing a VF display is a so-called head up display (HUD) system wherein at least some of the vehicle's operational information typically associated with the vehicle instrument cluster is projected onto the interior surface of the windshield with a multi-segment VF display unit. The vehicle operator may then obtain such information without diverting his/her line of vision from the road ahead. Typical information so displayed may include vehicle speed, engine RPM, fuel quantity remaining, and the like.
One downside of using a VF display in such a HUD application is that the VF display generally requires high voltages for sufficient illumination of the multiple segments (typically on the order of 60 volts). A high-voltage load driver integrated circuit (IC) or equivalent is thus required to provide high-voltage drive to the multiple display segments. Although such high-voltage load drivers are known, and readily available, their operation in such an application inherently generates significant electronic noise. It is known that such noise in the FM band (88 MHZ-108 MHZ) may be minimized via optimal circuit board layout and passive filtering, but noise in the AM band (500 kHz-1500 kHz) is generally not susceptible to significant reduction by using conventional techniques. As an example of such AM band noise generation, a known 32-bit high-voltage VF driver IC, operated in duplex mode to illuminate a VF HUD, typically radiates between 45 db.mu.v/m and 65 db.mu.v/m of noise in the AM band.
In the near future, radiated emission guidelines for automotive applications will require less than 28 db.mu.v/m of AM band noise per system. In order to meet such a requirement, a 20 db.mu.v/m-40 db.mu.v/m improvement must be made over known technology. What is therefore needed is a technique for reducing radiated emission from high-voltage load driver IC applications such as, for example, those used in VF HUD systems. The technique should ideally reduce radiated emissions to within acceptable levels, be easily integrated into existing systems, and be cost-effectively implemented.